1. Field of the Invention
The present invention relates to a backlight device, and more particularly, to an edge light type backlight device suitably used for a liquid crystal display.
2. Discussion of the Related Art
Research on flat panel displays continues to be performed. Among such flat panel displays are liquid crystal display (LCD) devices, field emission display (FED) devices, electro-luminescence display (ELD) devices, and plasma display panels (PDP).
In general, LCD devices are gaining popularity in monitors for notebook and desktop personal computers (PC's), and liquid crystal televisions because of their high contrast ratio, gray scale display suitable for displaying motion pictures, and their thin characteristics. However, LCD devices do not emit light on there own, and are provided with a separate external light source for irradiating light, e.g., a backlight device. The backlight device includes a projection type and an edge light type backlight devices. The edge light type backlight device being the most commonly used.
In the edge light type backlight device, a tube-shaped light source such as a fluorescent lamp (hot cathode, cold cathode) or the like is installed at a side portion of the LC panel, and the light from the fluorescent lamp is irradiated onto the entire surface of the LC panel screen using a transparent light guiding plate.
A liquid crystal display device according to the related art will be described with reference to the accompanying drawings.
FIG. 1 shows an LCD device according to the related art that includes a liquid crystal (LC) panel 100 comprising a thin film transistor (TFT) substrate 1, a color filter substrate 2, and a liquid crystal layer interposed therebetween, a driving circuit unit 101 for applying a voltage to the LC panel 100 and supplying a signal for driving the liquid crystal molecules of the liquid crystal layer, a backlight device installed below the LC panel 100 for transferring light irradiated from a lamp 111 towards the LC panel 100 through a light guiding plate 113, a frame for supporting the LC panel 100 and the backlight device, and a bezel part 104 coupled to the outer portions of the frame 105 to enclose the edge portions except for the effective display area where an image is displayed.
The lamp 111 functions as the light source and is located at an edge portion below the LC panel 100. In a monitor or LCD device for television requiring high luminance, two or more lamps 111 may be used as shown in FIG. 1.
FIG. 2 shows the backlight device which includes the lamp 11 installed at the left or right side for supplying light, a lamp housing 12 for fixing the lamp 11 and concentrating the light emitted from the lamp 11 towards the light guiding plate 13, a reflection sheet 14 arranged beneath the light guiding plate 13 for reflecting light leaked through an opposite direction to the LC panel toward the light guiding plate 13, a diffusion sheet 15 arranged on the light guiding plate 13 for uniformly diffusing the light emitted from the light guiding plate 13, a prism sheet 16 arranged on the diffusion sheet 15 for transferring the light diffused and concentrated by the diffusion sheet 15 to the LC panel, a protection sheet 17 arranged on the prism sheet 16 for protecting the prism sheet 16, and a main supporting frame 18 for receiving and fixing the aforementioned elements therein.
A scattering pattern 13a may be further included in the lower surface of the light guiding plate 13 for scattering light and emitting the scattered light toward the LC panel. Light emitted from the lamp 11 of the backlight device is concentrated on a light incident face of the light guiding plate 13, sequentially passes through the light guiding plate 13, the diffusion sheet 15, and the prism sheet 16, and is transferred to an information display surface. In the light emitted from the backlight device, the light reflected by an edge portion of the LC panel and the light directly emitted from the backlight device interfere with each other, thereby preventing the emission of light stronger than the surroundings, and resulting in a bright line along an edge of the effective light irradiation region.
In order to solve this bright line problem, a method for forming a printed portion for the removal of the bright line at a light incident part of a sheet of the backlight device, has been developed.
FIG. 3 is a cross-sectional view of a backlight device according to the related art. In FIG. 3 the backlight device includes a printed portion 19 formed at a light incident part of the reflection sheet 14 beneath the light guiding plate 13 for the removal of the bright light.
FIG. 4 is a cross-sectional view of printed portion 19 of the reflection sheet 14 according to the related art. In FIG. 4, the printed portion 19 of the reflection sheet 14 includes black or any other color formed by a dot printing method. Accordingly, the bright line at a specific portion of the light incident part is either absorbed or irregularly reflected by the dot printed portion 19. In addition, to remove the bright line the dot printed portion 19 may be formed on the light incident part of either the reflection sheet or the protection sheet. However, this method has several drawbacks. For example, if the printed portion is displaced, a defect appearing to be a black line on the display area occurs, also the dot printing process is complicated and costs associated the printing process is increased.
However, in case the printed portion is displaced, a failure appearing to be a black line on the effective display area is formed, and also the dot printing process and the costs associated with the process are increased.